Daniel Végh

CONDENSED O-, N-HETEROCYCLES BY THE TRANSFORMATION OF AZIDOACRYLATES

SummaryA number of furo[3,2-c]pyridines (4a–4d) and benzo[b]derivative (4e), as well as pyrrolo[2′,3′-4,5]furo[3,2-c]pyridine (8) were prepared by reaction of the corresponding iminophosphoranes, available from ethyl azidoheteroacrylates and triphenylphosphine, with phenyl isocyanate. The appropriate azidoheteroacrylates were used for the preparation of some substituted furo[3,2-b:4,5-b]dipyrroles (6). The reactions of the prepared compounds are described.ZusammenfassungEine Anzahl von Furo[3,2-c]pyridinen (4a –4d), ein Benzo[b]derivat (4e) und Pyrrolo[2′,3′:4,5]furo[3,2-c]pyridin (8) wurden durch die Reaktion von Phenylisocyanaten mit den entsprechenden Iminophosphoranen dargestellt, die aus Ethyl-azidoheteroacrylaten und Triphenylphosphin leicht zugänglich sind. Die entsprechenden Azidoacrylate wurden zur Synthese einiger Furo[3,2-b:4,5-b′]dipyrrole (6) verwendet. Die Reaktionen einiger dieser Verbindungen werden beschrieben.

Optical properties of furanic and thiophenic ethane-1,2-diones: A combined experimental and theoretical study

Abstract The syntheses, spectral measurements and the AM1 geometries of di-furan-2-yl-ethane-1,2-dione, di-thiophen-2-yl-ethane-1,2-dione, bis-[2,2′]-bithiophen-2,5-yl-ethane-1,2-dione and bis-[2,2′; 5′,2″]-terthiophen-2,5-yl-ethane-1,2-dione are presented. The electron absorption spectra for stable conformers are obtained by ZINDO/S method and they reasonably well agree with the experimental data. The increasing chain length influences the electronic polarizability and hyperpolarizabilities as demonstrated by the finite field method in AM1 approach.

Non-linear optical properties of new bridged bis-thienyls: I. Pyrazine-based bridges: theory, synthesis and spectra

Abstract The conformational analysis of 2,3-bis(2′-thienyl)pyrazine (A), 2,3-dicyano-5,6-bis(2′-thienyl)pyrazine (B), 2,3-difluoro-5,6-bis(2′-thienyl)pyrazine (C), 2,3-bis(2′-thienyl)furo[3,4-b]pyrazine (D), 2,3-bis(2′-thienyl)pyrrolo[3,4-b]pyrazine (E), 2,3-bis(2′-thienyl)thieno[3,4-b]pyrazine (F), 2,3-bis(2′-thienyl)quinoxaline (G), 2,3-bis(2′-thienyl)pyrido[3,4-b]pyrazine (H) and 2,3-bis(2′-thienyl)pyrido[2,3-b]pyrazine (I) is elaborated using semiempirical Austin Model 1 (AM1) method. The electron absorption spectra for stable conformers are calculated by ZINDO/S method. The influence of the bridge variations on the electronic polarisability and second hyperpolarisability is investigated using the time-dependent Hartree–Fock method in AM1 approach. The synthesis and spectral measurements of the most promising B, F, G and I compounds are presented. Our results indicate that the G and I ones seem to be suitable candidates for the subsequent preparation of the electro-optical materials.

Characterization and properties of the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine with 3-dodecylthiophene

Abstract The method of chemical oxidative polymerization with FeCl 3 was used to synthesize the copolymer of dipyrido-[3,2-a; 2′,3′-c]-thien-[3,4-c]azine (DPTA) and 3-dodecylthiophene (DDT). The copolymer was characterized by UV–VIS, Raman, 1 H and 13 C NMR and EPR spectroscopy. It has been found that the DPTA/DDT copolymer exhibits properties of the low-band-gap polymer ( E g

Marked stabilization of redox states and enhanced catalytic activity in galactose oxidase models based on transition metal S-methylisothiosemicarbazonates with -SR group in ortho position to the phenolic oxygen.

Reactions of 5-tert-butyl-2-hydroxy-3-methylsulfanylbenzaldehyde S-methylisothiosemicarbazone and 5-tert-butyl-2-hydroxy-3-phenylsulfanylbenzaldehyde S-methylisothiosemicarbazone with pentane-2,4-dione (Hacac) and triethyl orthoformate in the presence of M(acac)2 as template source at 107 °C afforded metal complexes of the type M(II)L(1) and M(II)L(2), where M = Ni and Cu, with a new Schiff base ligand with thiomethyl (H2L(1)) and/or thiophenyl (H2L(2)) group in the ortho position of the phenolic moiety. Demetalation of NiL(1) in CHCl3 with HCl(g) afforded H2L(1). The latter reacts with Zn(OAc)2·2H2O with formation of ZnL(1). The effect of -SR groups and metal ion identity on stabilization of phenoxyl radicals generated electrochemically was studied in detail. A marked stabilization of phenoxyl radical was observed in one-electron-oxidized complexes [ML(2)](+) (M = Ni, Cu) at room temperature, as demonstrated by cyclic voltammetry, EPR spectroscopy, and UV-vis-NIR measurements. In solution, the oxidized CuL(2) and NiL(2) display intense low-energy NIR transitions consistent with their classification as metal-delocalized phenoxyl radical species. While the CuL(2) complex shows reversible reduction, reduction of NiL(2), CuL(1), and NiL(1) is irreversible. EPR measurements in conjunction with density functional theory calculations provided insights into the extent of electron delocalization as well as spin density in different redox states. The experimental room temperature spectroelectrochemical data can be reliably interpreted with the (3)[CuL(2)](+) and (2)[NiL(2)](+) oxidation ground states. The catalytic activity of synthesized complexes in the selective oxidations of alcohols has been studied as well. The remarkable efficiency is evident from the high yields of carbonyl products when employing both the CuL(2)/air/TEMPO and the CuL(2)/TBHP/MW(microwave-assisted) oxidation systems.

Optical properties of 2,3-diaza-1,3-butadiene bridged oligothiophenes A combined experimental and theoretical study

Abstract The syntheses, spectral measurements and the AM1 (Austin model 1) geometry optimisation of N , N ′-bis-thiophen-2-ylmethylene-hydrazine ( IIIa ), N , N ′-bis-(3-methyl-thiophen-2-ylmethylene)-hydrazine ( IIIb ), N -[2,2′]-bithiophen-5-ylmethylene- N ′-thiophen-2-ylmethylene-hydrazine ( IIIc ), N , N ′-bis-[2,2′]-bithiophen-5-ylmethylene-hydrazine ( IIId ), N -[2,2′; 5′,2″]-terthiophen-5-ylmethylene- N ′-thiophene-2-ylmethylene-hydrazine ( IIIe ), N -[2,2′]-bithiophen-5-ylmethylene- N ′-[2,2′; 5′,2″]-terthiophen-5-ylmethylene-hydrazine ( IIIf ) and N , N ′-bis-[2,2′; 5′,2″]-terthiophen-5-ylmethylene-hydrazine ( IIIg ) are elaborated. The electron absorption spectra for all- trans conformers are obtained by ZINDO/S method and compared with the experimental data. The influence of the chain length on the electronic polarisability and second-order hyperpolarisability is investigated using the time-dependent Hartree–Fock method in AM1 approach.

Spectral characteristics of bisthiophenes and terthiophenes linked with heterocyclic unit in solution and polymer matrix

Abstract Spectral characteristics of derivatives of thiophene substituted on hetoroaromatic cycle as pyrazine was compared with terthiophene linked with cyano and hydrazo groups. The absorption, fluorescence and its lifetime were measured in solution (methanol, cyclohexane) and in polymer matrices (polystyrene, PS; polymethyl methacrylate, PMMA; and polyvinyl chloride, PVC). Derivatives with two thiophene units substitute on pyrazine exhibit the lowest wavenumber band in the region 26,320–25,600xa0cm −1 and logxa0 e ∼4.0, which is not influenced by the medium. Derivatives with benzene and pyridine ring annealed to pyrazine (2,3-bis-(2′-thienyl)quinoxaline ( I ), 2,3-bis-(2′-thienyl)pyrido[2,3-b]pyrazine ( III )) exhibit fluorescence in polar methanol with maximum at 22,200xa0cm −1 and quantum yield of about 0.2 which is blue-shifted in going to non-polar solvent. The maximum fluorescence is slightly blue-shifted in polymer matrices as compared to methanol. Derivatives with annealed thiophene to pyrazine or substituted with two cyano groups (2,3-bis-(2′-thienyl)thieno[3,4-b]pyrazine ( II ), 2,3-dicyano-5,6-bis(2′-thienyl)pyrazine ( IV )) do not yield any emission. Derivatives with terthiophene structural units ([2,2′,5′,2″]-terthiophene-[2]-thienylacrylonitrile ( V ) [2,2′,5′,2″]-terthiophene-5-carbaldehydehydrazone ( VI )) exhibit fluorescence with maximum around 20,000xa0cm −1 . The lifetime of fluorescence of all thiophene was 1xa0ns or shorter. The polymer matrices increase the intensity of fluorescence to some extent and prolong the lifetime of thiophene derivatives. Derivative VI exhibits some tendency to an aggregation at higher concentration above 0.01xa0molxa0kg −1 in polymer matrices.

Conformational transition in polypyrrole at low pressure

Abstract Electrical conductivity and infrared spectra of doped polypyrrole react to variations of pressure below atmospheric pressure, A glass transition, related to the variation of pressure, can be observed in the temperature dependence of the conductivity and infrared spectra. The existence of the glass transition supports the interpretation of the pressure effect as a conformational coil-rod transition.

Synthesis of the copolymer of 2,3-di(1-tridecyl)thieno[3,4-b]pyrazine with 3-dodecylthiophene using the chemical oxidation with iron trichloride

Abstract By applying the method of chemical oxidative polymerization with FeCl 3 the copolymer of 2,3-bis-tridecylthieno[3,4- b ]-pyrazine (TTP) and 3-dodecylthiophene (DDT) was synthesized. The copolymer was characterized by the UV–VIS, FT-IR, 1 H -NMR, 13 C -NMR and EPR spectroscopy. The product is soluble in a common organic solvent (chloroform, dichloroethane, tetrahydrofurane, and toluene). The copolymer with a higher TTP content exhibits the properties of the low-band-gap polymers with an absorption edge above 900 nm (1.38 eV).

Spectral characteristics of carbonyl substituted 2,2′-bithiophenes in polymer matrices and low polar solvents

The spectral characteristics of monosubstituted derivatives of 2,2-bithiophene (1-BT) with simple carbonyl substituents, including -COCF3 (trifluoroacetyl, 2-BTCF), -COCH2CN (oxopropanenitrile, 3-BTCN) and -COCH3 (acetyl, 4-BTCE), and the more complex 5-((9H-fluoren-9-ylidene)methyl)-3-methyl, 5-methyl carboxylate (5-BTFL) were investigated. Absorption and fluorescence spectra and fluorescence lifetimes were measured in solvents with various polarities and compared with those in polymer matrices (polystyrene, PS; polymethyl methacrylate, PMMA; and polyvinyl chloride, PVC). Although the parent, 1-BT, absorbed near 300 nm and exhibited no or weak fluorescence, the substitution of 1-BTwith simple substituents at position 5 resulted in a bathochromic shift of approximately 50 nm or more in absorption and distinct fluorescence above 400 nm. The largest shift in absorption and fluorescence was observed for the complex 5-BTFL with fluorene as a substituent for 1-BT. The most intense fluorescence was observed for the derivative 2-BTCF with trifluoroacetyl as a substituent in the polar PVC matrix. The lifetimes of fluorescence of all substituted 2,2-bithiophenes were in the range from 0.3 to 3 ns. The polymer matrices increased the intensity of fluorescence to some extent and prolonged the lifetime of the 2,2-bithiophene derivatives. The reasons for the variation in the fluorescence intensity resulting from the substitution of the parent dimer are discussed.